New to me truck. 2014 6.2, 4X4. 61K. Now this may be completely normal but that is why I am asking. I have had the truck for going on a month now. Since the hot weather has kicked in I have noticed that when the truck sits out in the sun for a while, when I start it up there is a new noise. It doesn't kick in right away. It may take a minute. It sounds like an old compressor kicking on. The truck gets considerably louder. It seems that once the AC has cooled the interior down and the engine gets up to operating temp it kicks off. It does not come back until the truck has sat for a while. The last two days have been much more mild and the old compressor noise has not happened. When I say old compressor, it doesn't sound rough. Just louder. Normal? Vacuum leak?
The AC blows cold and strong like it should.

The fan clutch engages at a pre determined temp. When it does, it engages the fan blades to pull air through the condenser and radiator. When this happens, the blades made more noise. When it cools down the noise goes away until it needs to pull more air through.

The fan clutch engages at a pre determined temp. When it does, it engages the fan blades to pull air through the condenser and radiator. When this happens, the blades made more noise. When it cools down the noise goes away until it needs to pull more air through.

Thanks cap'n. I just googlered it. Is there a way to confirm this without ripping it apart. It looks like a relatively easy, driveway replacement.

My brothers F150 did the same thing. His wife drove it for a week and kept saying it was really loud etc so he drove it and seemed normal but she swore something was wrong so he took it to the shop to get it checked out. Apparently from what he was told is that depending upon the engine or something that there can be a normal clutch and a performance clutch on the vehicle. The performance clutch is stronger and louder. with yours having the 6.2 i would suspect it might have a larger/performance clutch. this is what he was told and i make no claims that it is true or i have a clue what im talking about at any time

I had something similar a couple of months ago but the noise wouldn't go away once it kicked on. Mine ended up being a leak in my radiator hose. I went ahead and replaced all of the hoses (Pretty easy job and I'm no mechanic) and I haven't had any issues since.

You have electric fans. One of my co workers drove his 2015 F-150 through deep water during Harvey, and noticed after that, his truck would get really loud in the same conditions you are talking about.

He took it in. Turned out the main radiator fan fuse blew, and so the truck was using an aux (backup) fan, which was considerably louder, to cool the truck down. Once they replaced the fuse, the sound stopped.

There is a good chance that when you said it didn't do it again until it sat for a while, that when driving your just not hearing it. Sometimes I can hear the clutch kicking in and sometimes I can't when driving.

My 2013 F150 did the same thing for the first time last Summer. I was concerned also since it had never done it for the first three years of owning it. It did it during the peak of the summer, but it has not done it since. Basically what I found through my research was the following response "Would you rather have a loud fan cooling down your engine, or for your truck to overheat?"